The present invention relates generally to an electrically conductive plastic rack for pipette tips, and more particularly, it relates to an electrically conductive plastic rack for use with pipette tips following removal of the pipette tips from a plurality of pipettes.
Modem laboratory automation often involves conducting experiments using plates having multiple wells. These plates are known as “microplates”. A typical microplate may contain three hundred and eighty four (384) wells or more. The microplate wells are used to hold specimens to be tested in a laboratory experiment. Pipettes are used to transfer liquids in and out of the microplate wells during the laboratory experiments. For example, the pipettes may transfer the initial specimens into the wells along with a number of different chemical reagents used during the laboratory experiment.
To prevent contamination of the pipettes when transferring liquid into and out of the microplate wells, a disposable polypropylene pipette tip is attached to the end of each pipette. The pipette tip carries all of the liquid to be transferred from one location to another, and prevents the actual pipette from contacting the liquid. After the transfer, the pipette tip is removed from the pipette and a new pipette tip is attached to the end of the pipette for subsequent transfers of different liquids. In this manner, precise concentrations, ingredient mixtures and amounts of liquids may be transferred using each pipette without the fear of contamination from a previous liquid transfer using the same pipette.
Multiple pipette devices are often used when conducting experiments using multiple well microplates. For example, a robotic device having three hundred eighty four (384) pipettes may be used when conducting experiments using a three hundred eighty four (384) well microplate. Such multiple pipette devices provide for the rapid removal or insertion of liquid into every microplate well. When using multiple pipette devices, tip racks are used to hold the pipette tips to be attached to the ends of the pipettes. The tip racks hold the tips in an organized fashion and allow the tips to be quickly inserted onto the pipettes or removed from the pipettes. Like the pipette tips, the tip racks are typically formed of polypropylene for ease of manufacture and cost savings. Because the tips and racks are both formed of relatively low cost polypropylene, it is customary in the industry to discard the tips and racks after a short period of time, or even after one use, for disposal and/or recycling.
With reference now to FIG. 1, the head 20 of a multiple pipette device 24 is shown. The head 20 holds three hundred eighty four pipettes 22 used to transfer liquid to and from a three hundred eighty four well microplate 50. Pipette tips 30 are shown inserted on each pipette 22 of the multiple pipette device 24. The pipette tips are positioned above a tip rack 40 used to hold the pipette tips 30 when they are removed from the pipettes 22 of the multiple pipette device 24.
Before the pipettes may be used to transfer liquid to and from the microplate wells, the tips 30 must be loaded onto the pipettes. A robotic arm (not shown) typically delivers a rack 40 full of tips 30 to the loading area 42. The head then positions itself directly above the rack 40 with each pipette in alignment with one of the tips 30. The head 20 then moves downward to bring the pipettes into contact with the tips 30. Each tip 30 is secured to a pipette with a friction-fit. Thus, the head must press (or be pulled) down with a substantial force to cause the tips to slide on to the ends of the pipettes. The sliding action of the polypropylene tips against the metal mandrels causes an electrostatic charge, i.e., triboelectricity, to develop on the exterior of the tips 30.
Once the tips are loaded onto the pipettes 22, the head 20 moves the pipettes and connected tips 30 to position the tips in the wells of the microplate 50. The pipettes then suck liquid from the wells and into the tips 30 for delivery to another location. After transferring liquid from one location to another (e.g., one microplate to another), the head returns to a position above the rack 40 so the head 20 is in position to return the used tips 30 to the rack. A shuck plate (not shown) then forces the tips from the pipettes, causing the tips 30 to fall into the tip rack 40 such that each tip is positioned in a tip seat on the tip rack. Of course, as the tips 30 are forced from the pipettes, they slide along the pipettes, once again causing an electrostatic charge to be generated and deposited upon the tips as a result of the rubbing action between the tips and the pipette. After the tips 30 are returned to the tip rack 40, the robotic arm may remove the rack full of tips for disposal or cleaning. Alternatively, the tips and rack may remain in place on the loading area for further use by the multiple pipette device.
Unfortunately, once the tips are returned to the rack, the triboelectric effect often creates a problem with the tips in the tip rack. In particular, when the polypropylene tips are returned to the polypropylene rack they each contain an electrostatic charge as a result of the rubbing action between the pipettes and tips during loading and unloading of the tips on the pipettes. The polypropylene tip rack does not conduct electricity. Thus, the static charges remain on the tips as they sit in the rack because there is no flow of the electric charge from the tips to the tip rack. The static charges on different tips and the rack itself cause some of the tips to repel away from each other and the rack. When the electrostatic charge is sufficient, this repelling action may cause one or more of the light-weight tips to become dislodged from the proper tip seats within the rack. In the worst situations, one or more tips may jump completely out of the tip rack as a result of the electrostatic forces between tips. When a tip becomes dislodged from a tip seat or jumps completely out of the tip rack, significant problems arise because loose tips may be lost and not properly discarded and removed from the testing area. Also, if in a subsequent step of a laboratory process the head is scheduled to return to the tip rack and once again join the pipettes to the used set of tips, an improperly seated tip on the tip rack may be crushed by the force of the head as the head moves the pipettes into position to pick up the tips. This may result in operational failure of the multiple pipette device and/or faulty experiment results.
For the foregoing reasons there is a need for a multiple pipette system that will prevent tips from becoming displaced in the tip rack as a result of the triboelectric effect during loading and unloading of the tips. In addition, there is a need for a tip rack for use with a multiple pipette system that will prevent electrically charged tips from becoming displaced within the rack.